It is desirable to recycle paper and packaging materials to reduce waste and reuse valuable natural resources. Recovered paper and packaging materials are subjected to several processes to remove ink, toner, and other contaminants such as glue and plastics that are commonly found on used paper and packing materials. The glue, plastics, and other similar contaminants are generally referred to as “stickies” by those skilled in the art. It is desirable for the ink, toner, and stickies to be removed before the recovered paper and packing materials are introduced into, for example, a paper-making machine.
If stickies are not properly removed, the stickies can adhere to the paper-making machine and create holes or weak spots in the reconstituted paper formed by the recovered paper and packaging material. Further, residual ink and toner particles can appear as blemishes in the reconstituted paper. Blemishes generally reduce the value of reconstituted paper.
A disperser, which is also known as a disperger, is a machine that processes recovered paper and packaging material for use in making paper or other products. Dispersers help remove ink, toner, and stickies from fibers, and reduce the particulate size of stickies in the recovered paper and material.
A conventional disperser typically includes a rotating rotor disc opposing a stationary stator disc. Each disc typically includes an assembly of pie-shaped plate segments arranged in a circular array to form a plate and mounted on a disc substrate, thereby creating the dispersing disc. The pie-shaped plate segments may be similar in shape to a truncated wedge formed by a minor sector of a circle. The front surface of each plate, which faces the front surface of the opposing plate, typically includes pyramids or teeth arranged in rows extending generally circumferentially across the plate. The circumferential rows of teeth or pyramids on one plate intermesh, e.g., are interlaced, interleave, or are staggardly interposed, between the rows of the teeth or pyramids on the opposing plates in a complementary manner. The rows are arranged at radii which allow the rows of pyramids or teeth on the plates mounted on the rotor and stator disc substrate to intersect a plane between the discs. This plane can be parallel to the front surface of the discs.
The intersection of the plane by the rows of teeth and/or pyramids enhance the impacts by the teeth and pyramids on the fibers of the recovered paper and packing material moving from the center of the stator disc to the periphery of the discs. The design of the disperser plate pyramids or teeth is referred to as “intermeshing tooth patterns”. These teeth and pyramids are generally part of the mold for the entire disc, disc segments, cone, or cone segments. Therefore, these teeth and pyramids are generally formed when the original disc, disc segment, cone, or cone segment is cast. These teeth and pyramids also extend outward from the front surface of each plate. The gap, i.e. the clearance between the pyramids or teeth of the rotor and stator discs is usually in a range of 1 to 6 millimeters (mm). The gap generally has a zigzag shape formed by the intermeshing rows of the teeth of the opposing plates. A conventional disperser plate is described in U.S. Pat. No. 7,172,148.
The gap of a typical intermeshing tooth disperser plate design allows a relatively thick fiber pad to form between the opposing faces of the rotor and stator plates. The teeth and pyramids act on the fibers in the pad. In a disperser, the fibers of the recovered paper or packing material are not cut or refined. The fibers are severely and alternately flexed by the action of the intermeshing patterns of teeth or pyramids on opposing front surfaces of a disperser plate. This action breaks the stickies into smaller particles. The smaller particles of the stickies may collect fine fiber particles that are further passivated as smaller particles.
An alternative conventional disperser uses conical surfaces rather than the planar surfaces of the discs. The rotating rotor is a cone having an outer surface with teeth. A stator is stationary and has a conical shape with an inside surface with rows of teeth or pyramids. The inside surface faces the outer surface of the rotor such that the rows of teeth or pyramids on the stator are intermeshed, that is staggardly interposed with the rows of teeth or pyramids on the rotor in a complementary manner. Teeth and pyramids are part of the mold for the entire cone or cone segment. Therefore, these teeth and pyramids are generally formed when the original cone or cone segment is cast.
In contrast to recovering paper and packaging material, fresh pulp for paper and paper based packaging materials is typically formed or developed using a mechanical refiner. Mechanical refiners may comprise refiner plate segments arranged in a circular array to form a plate; plates are generally mounted on disc substrates, on opposing discs. The discs may be flat (planar) or conical. The opposing plates mounted on the opposing discs may both rotate or one may be stationary while the other rotates.
Mechanical refiners, in contrast to dispersers, refine lignocellulosic material, such as wood chips, wood pulp, or other cellulosic material, by separating fibers in the lignocellulosic material. Refiner plates typically have a front face with a pattern of bars and grooves arranged in one or more refining fields. The bars have precision machined top surfaces. The feed material, lignocellulosic material such as wood chips or other cellulosic material, moves through a gap between the tops of the bars on opposing plates on the opposing discs. The gap is typically less than 1 mm. The refining action occurs as feed material passes generally radially outwardly through the gap between the opposing relatively rotating discs. The feed material is refined as it moves radially outward through the small gap between the discs and is impacted as opposing bars cross each other. The feed material also moves radially outward through the grooves between the bars extending radially. As the material moves from the inner portion of the discs to the outer region of the discs, the crossing of the bars allows for developing and cutting of the feed material.
The bar and groove patterns of refiner plates and resulting impacts due to the crossing of bars is suited for refining of lignocellulosic material. A benefit of discs in a conventional mechanical refiner is the high compression action discs can impart to the material within the refiner due to the small gap (typically less than 1 mm) and crossing of the bars, resulting in development of enhanced fiber bonding properties.
However, bar and groove patterns of refiner plates mounted on the discs of a conventional mechanical refiner are not well-suited to processing recovered paper and packaging material, in part, because the presence of ink and stickies. To remove stickies, dispersers require a thick fiber pad to form between the plates; the required thick fiber pad is not achieved with conventional bar and groove patterns. Conventional bar and groove patterns usually create a relatively evenly distributed thin fiber pad in the gap. A thick fiber pad is needed in view of the dispersion action of the intermeshing pyramids or grooves. The bars of a conventional mechanical refiner plate are not well-suited to creating the thick fiber pad needed for optimal dispersion action. Furthermore, the frequency at which bars cross in a typical or conventional mechanical refiner would be too high to adequately break up the stickies.